Liquid crystal display device

ABSTRACT

The present invention provides a liquid crystal display device used as a display part of an electronic apparatus which exhibits high brightness and favorable display quality. The liquid crystal display device includes a pair of substrates which are arranged to face each other in an opposed manner; vertical-alignment type liquid crystal which is sealed between the pair of substrates; a plurality of pixel regions, each pixel region including a sub pixel having a pixel electrode on one substrate and a sub pixel having a pixel electrode on one substrate, a slit formed between the pixel electrodes; and a singular point control part which includes projecting portions which are formed on end portions of the pixel electrodes on the slit-side and controls singular points of the liquid crystal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device used ina display part of an electronic apparatus or the like.

2. Description of the Related Art

FIG. 13 shows the schematic cross-sectional constitution of aconventional liquid crystal display device. As shown in FIG. 13, theliquid crystal display device includes a TFT substrate 102 on which athin film transistor (TFT) and a pixel electrode are formed for everypixel, and a counter substrate 104 on which color filters (CF) and acommon electrode are formed. Both substrates 102, 104 are laminated toeach other through a sealing material 152 which is applied to outerperipheral portions of both substrates 102, 104. A mounting terminal 160which serves to mount a driver IC is formed on the TFT substrate 102.Liquid crystal 106 is sealed between both substrates 102, 104. A cellgap defined between both substrates 102, 104 is held by sphericalspacers 146, for example. Further, polarizers 187, 186 are arranged onthe outsides which sandwich both substrates 102, 104 therebetween.

FIG. 14 shows the constitution of one pixel of a conventional MVA(Multi-domain Vertical Alignment) type liquid crystal display device. Asshown in FIG. 14, the liquid crystal display device includes a pluralityof gate bus lines 112 which are formed on the TFT substrate 102, and aplurality of drain bus lines 114 which intersect the gate bus lines 112through an insulation film. TFTs 120 are formed in the vicinity ofpositions where the gate bus lines 112 and the drain bus lines 114intersect each other. In a pixel region which is defined by the gate buslines 112 and the drain bus lines 114, a pixel electrode 116 is formed.A storage capacitor bus line 118 which extends parallel to the gate busline 112 is formed in a state that the storage capacitor bus line 118transverses the pixel region. A storage capacitor electrode 119 isformed over the storage capacitor bus line 118 through an insulationfilm for every pixel. A linear slit (blank on an electrode) 144 whichextends obliquely with respect to polarization axes of the polarizers186, 187 is formed on the pixel electrode 116. On the counter substrate104 side, linear projections 142 which extend parallel to the slit 144are formed. The slit 144 and the linear projections 142 function as thealignment regulating structure which regulates the alignment of theliquid crystal 106.

FIG. 15A and FIG. 15B are cross-sectional views for explaining thealignment regulating structure. In FIG. 15A and FIG. 15B, linearprojections 143 are formed on the substrate 102, while the linearprojections 142 are formed on the substrate 104. As shown in FIG. 15A,the linear projections 143 on the TFT substrate 102 side are formed onan alignment film 150 which is formed on the pixel electrode 116, forexample. The linear projections 142 of the counter substrate 104 sideare formed on an alignment film 151 which is formed on a commonelectrode 141, for example. At the time of applying no voltage, liquidcrystal molecules 108 are aligned substantially normal to surfaces ofthe substrates. When a voltage is applied between the pixel electrode116 and the counter electrode 141, as shown in FIG. 15B, the liquidcrystal molecules 108 are tilted. Using the linear projections 142, 143as boundaries, the direction that the liquid crystal molecules 108 aretilted differs and the liquid crystal molecules 108 in a region betweenthe neighboring linear projections 142, 143 are tilted in the samedirection. By arranging the alignment regulating structure as shown inFIG. 14, the liquid crystal molecules 108 are tilted in four directionsorthogonal to each other in the inside of one pixel. Due to such analignment division technique, the deviation of a viewing angle which isa phenomenon generated in the liquid crystal display device in which theliquid crystal molecules 108 are tilted only in one direction can beeliminated thus largely improving the viewing angle characteristics.Here, in the constitution shown in FIG. 15A and FIG. 15B, the linearprojections 142, 143 are formed on both substrates 102, 104 as thealignment regulating structure. However, there may be a case that thelinear projections are formed on only one of the substrates 102, 104.Further, there may be a case that slits are formed on both substrates102, 104 in place of the linear projections 142, 143. Still further,there may be case that slits 145 are formed only one of substrates 102,104 as shown in FIG. 16.

FIG. 17 shows one pixel of a general MVA type liquid crystal displaydevice in which slits 144 are formed in a TFT substrate 102 side andlinear projections 142 are formed on the counter substrate 104 side.FIG. 18 shows the cross-sectional constitution of the liquid crystaldisplay device taken along a line X-X in FIG. 17, while FIG. 19 showsthe cross-sectional constitution of a TFT substrate 102 taken along aline Y-Y in FIG. 17. As shown in FIG. 17 to FIG. 19, a pixel electrode116 is divided into several regions by slits 144, and the respectiveregions of the pixel electrode 116 in the inside of the pixel areelectrically connected with each other thus maintaining the respectiveregions at the same potential. The pixel electrode 116 is connected witha source electrode 122 of a TFT 120 via a contact hole 123 and also iselectrically connected with a storage capacitor electrode 119 via acontact hole 126. A drain electrode 121 of the TFT 120 is electricallyconnected with a drain bus line 114. Due to the formation of the slits144 and linear projections 142, the pixel region is divided into fouralignment regions α to δ which differ from each other in the alignmentazimuth of liquid crystal molecules 108.

FIG. 20 schematically shows the alignment azimuths of the liquid crystalmolecules 108 in the respective alignment regions α to δ and an arearatio of the respective alignment regions in the inside of one pixel. Asshown in FIG. 20, areas of the respective alignment regions α to δ whichdiffer in the alignment azimuth of the liquid crystal molecules 108 fromeach other are set substantially equal in the inside of one pixel.Accordingly, the viewing angle characteristics of the liquid crystaldisplay device do not posses the large dependency on an azimuth angle ofa display screen and hence, a favorable display is obtained from anyazimuth.

FIG. 21 shows the constitution of one pixel of a liquid crystal displaydevice in which the arrangement of the slits 144 and the linearprojections 142 is exchanged with respect to the constitution shown inFIG. 17 to FIG. 19. FIG. 22 shows the cross-sectional constitution ofthe liquid crystal display device taken along a line Z-Z in FIG. 21.Also in the liquid crystal display device shown in FIG. 21 to FIG. 22,the areas of the alignment regions α to δ are set substantially equal inthe inside of one pixel. Accordingly, in the same manner as the liquidcrystal display device shown in FIG. 17 to FIG. 19, it is possible toobtain a favorable display from any azimuth.

FIG. 23 is a graph showing the transmissivity characteristics (T-Vcharacteristics) with respect to an applied voltage of a liquid crystaldisplay device adopting a VA (vertically aligned) mode. The appliedvoltage (V) to a liquid crystal layer is taken on an axis of abscissasand the transmissivity of light is taken on an axis of ordinates. A lineL indicates the T-V characteristics in the direction normal to a displayscreen (hereinafter referred to as “front direction”), and a line Mindicates the T-V characteristics in the direction of an azimuth angleof 90° and a polar angle of 60° with respect to the display screen(hereinafter referred to as “tilted direction”). Here, the azimuth angleis an angle which is measured in the counter clock direction using theright direction of the display screen as the difference. Further, thepolar angle is an angle which is made with a perpendicular which iserected on the center of the display screen.

As shown in FIG. 23, in the vicinity of a region surrounded by a circleN, a distortion is generated in the change of the transmissivity(brightness). For example, although the transmissivity in the obliquedirection is higher than the transmissivity in the front direction at arelatively low gray scale with the applied voltage of approximately 2.5V, the transmissivity in the tilted direction is lower than thetransmissivity in the front direction at a relatively high gray scalewith the applied voltage of approximately 3.8 V. As a result, whenviewed from the tilted direction, the brightness difference within aneffective drive voltage range becomes small. This phenomenon appearsmost conspicuously in the color change.

FIG. 24A and FIG. 24B show the change of appearance of an imagedisplayed on a display screen. FIG. 24A shows the image as viewed fromthe front direction, and FIG. 24B shows the image as viewed from thetilted direction. As shown in FIG. 24A and FIG. 24B, when the displayscreen is viewed from the tilted direction, the color of the image ischanged to a whitish color compared to the viewing from the frontdirection.

FIG. 25A to FIG. 25C show gray scale histograms of three primary colorsof red (R), green (G), blue (B) in a reddish image. FIG. 25A shows thegray scale histogram of R, FIG. 25B shows the gray scale histogram of G,and FIG. 25C shows the gray scale histogram of B. In FIG. 25A to FIG.25C, the gray scales (256 gray scales from 0 to 255) are taken on anaxis of abscissas and an existence ratio (%) is taken on an axis ofordinates. As shown in FIG. 25A to FIG. 25C, in the image, R at therelatively high gray scale and G and B at the relatively low gray scalesexist at high existence ratios. When such an image is displayed on adisplay screen of a liquid crystal display device adopting a VA mode andis observed from the tilted direction, R of high gray scale is changedin a relatively dark mode, while G and B of low gray scales are changedin the relatively bright mode. Accordingly, the brightness difference ofthree primary colors becomes small and hence, the color of the wholescreen becomes whitish as viewed from the tilted direction thus givingrise to a drawback that the color reproducibility is lowered.

To overcome the above-mentioned drawback, there has been proposed afollowing technique. That is, one pixel is divided into a plurality ofsub pixels and pixel electrodes which are separated from each other areprovided to the respective sub pixels. The respective pixel electrodesestablish the electrically capacitive coupling relationship. Forexample, the pixel electrode of the sub pixel A is directly connected toa source electrode of a TFT, and the pixel electrode of the sub pixel Bis connected to the source electrode via a predetermined controlcapacitance Cc. When the TFT which is formed for every pixel assumes anON state, a potential is divided according to the capacitance ratio andhence, voltages which differ from each other are applied to the pixelelectrodes of the respective sub pixels. Accordingly, the voltage isapplied to the liquid crystal layer for every sub pixel. In this manner,when the plurality of sub pixels which differ in the voltage applied tothe liquid crystal layer are present in the inside of one pixel, thedistortion of the T-V characteristics shown in FIG. 23 is dispersed intothe plurality of sub pixels. Accordingly, it is possible to suppress thephenomenon that the image becomes whitish as viewed from the tilteddirection and hence, the viewing angle characteristics are improved.Hereinafter, the above-mentioned technique is referred to as acapacitive coupling HT (halftone-gray scale) method.

FIG. 26 shows the constitution of one pixel of a conventional MVA typeliquid crystal display device which uses the capacitive coupling HTmethod. As shown in FIG. 26, a pixel region includes a sub pixel A and asub pixel B. In the sub pixel A, a pixel electrode 116 is formed on aTFT substrate 102, while in the sub pixel B, a pixel electrode 117 whichis separated from the pixel electrode 116 is formed on the TFT substrate102. The pixel electrode 116 is electrically connected with a storagecapacitor electrode 119 and a source electrode 122 of a TFT 120 viacontact hole 124. On the other hand, the pixel electrode 117 assumes anelectrically floating state. The source electrode 122 is electricallyconnected with the storage capacitor electrode 119 via a controlcapacitance electrode 125. The pixel electrode 117 has a region which isoverlapped to the control capacitance electrode 125 through a protectivefilm (insulation film) and is indirectly connected with the sourceelectrode 122 by capacitive coupling via a control capacitance Cc whichis formed in the region.

Between the pixel electrodes 116, 117, a slit 144 which extendsobliquely with respect to an end portion of the pixel region is formed.The slit 144 separates the pixel electrodes 116, 117 from each otherand, at the same time, also functions as the alignment regulatingstructure which regulates the alignment of liquid crystal 106.

A counter substrate 104 which is arranged to face the TFT substrate 102in an opposed manner with a liquid crystal layer therebetween includes acommon electrode 141 (not shown in FIG. 26). A liquid crystalcapacitance Clc1 is formed between the pixel electrode 116 of the subpixel A and the common electrode 141, while a liquid crystal capacitanceClc2 is formed between the pixel electrode 117 of the sub pixel B andthe common electrode 141. On the common electrode 141, a linearprojection 142 which extends parallel to the slit 144 and functions asthe alignment regulating structure is formed. The control capacitanceelectrode 125 on the TFT substrate 102 side is arranged to be overlappedto the linear projection 142 as viewed in the direction normal tosurfaces of the substrates. Further, on the counter substrate 104, alight shielding film (BM) 145 which shields a pixel region end portionfrom light is formed.

Assume that the TFT 120 is turned on so that a voltage is applied to thepixel electrode 116 and a voltage Vpx1 is applied to the liquid crystallayer of the sub pixel A. Here, since the potential is divided inaccordance with the capacitance ratio between the liquid crystalcapacitance Clc2 and a control capacitance Cc, a voltage which isdifferent from a voltage applied to the pixel electrode 116 is appliedto the pixel electrode 117 of the sub pixel B. A voltage Vpx2 which isapplied to the liquid crystal layer of the sub pixel B is expressed asfollows.

Vpx2=(Cc/(Clc2+Cc))×Vpx1

Here, since a relationship 0<(Cc/(Clc2+Cc))<1 is established, arelationship |Vpx2|<|Vpx1 | is established except for Vpx1=Vpx2=0. Inthis manner, in the liquid crystal display device having the pixelstructure shown in FIG. 26, it is possible to make the voltage Vpx1applied to the liquid crystal layer in the sub pixel A and the voltageVpx2 applied to the liquid crystal layer in the sub pixel B differentfrom each other in the inside of one pixel and hence, the viewing anglecharacteristics can be improved.

FIG. 27 shows the constitutions of the pixel electrodes 116, 117 in thevicinity of the slit 144. FIG. 28 shows a display state of the sameregion as FIG. 27 when the pixel is displayed in white. In FIG. 28, anexample of polarization axes 186 a, 187 a of polarizers 186, 187 isshown together with a region. FIG. 29 schematically shows the alignmentof liquid crystal molecules 108 in a region inside a circle P in FIG.28. As shown in FIG. 27 to FIG. 29, the liquid crystal molecules 108 ato which a voltage is applied are respectively tilted normal to theextending direction of the slit 144 and, at the same time, in thedirections opposite from each other using the slit 144 (and the linearprojection 142) as a boundary. However, although the liquid crystalmolecules 108 b, 108 c in the region above the slit 144 are tiltedparallel to the direction that the slit 144 extends, the liquid crystalmolecules 108 b, 108 c are not regulated with respect to the side towhich they are tilted. In the region above the slit 144, the liquidcrystal molecules 108 b which are tilted downwardly in FIG. 29 and theliquid crystal molecules 108 c which are tilted upwardly exist andhence, nodes (singular points) 162 a, 162 b of the liquid crystalalignment are formed. The singular points 162 a, 162 b are formed atrandom positions above the slits 144 and hence, the control of theformation positions is difficult. Further, there may be a case that thesingular points 162 a, 162 b are moved along with a lapse of time. Sincethe spatial and long-period fixing of the formation positions of thesingular points 162 a, 162 b is difficult, after a black display isperformed, there may be a case in which the formation positions of thesingular points 162 a, 162 b differ between a state in which white isdisplayed through an intermediate gray scale display and a state inwhich white is displayed immediately after the black display. That is,even these white displays are the same, they pass through the differentvoltage applying histories and hence, they differ in the positions ofthe singular points 162 a, 162 b whereby the display becomes differentdepending on the viewing direction of the screen. Further, when apressure is locally applied to the display screen with finger pushing orthe like and the alignment of the liquid crystal is disturbed, there maybe a case that an original alignment state cannot be restored. In thismanner, the conventional liquid crystal display device has a drawbackthat a favorable display quality can not be achieved.

Here, between a drain bus line 114 and the pixel electrodes 116, 117, agiven electric capacitance is formed. In the constitution in which anovercoat layer having a large film thickness is not formed as a layerbetween the drain bus line 114 and the pixel electrodes 116, 117, due tothe difference in distance within a substrate plane between the drainbus line 114 and the pixel electrodes 116, 117, a value of the formedelectric capacitance is liable to be easily changed. Accordingly, when arelative patterning displacement is generated with respect to the drainbus line 114 and the pixel electrodes 116, 117 due to shotirregularities which occur when the division exposure is performed orthe like, for example, in the manufactured liquid crystal displaydevice, the display irregularities which differ in displaycharacteristics for every division exposure region are observed withnaked eyes. Accordingly, it is necessary to separate end portions of thepixel electrodes 116, 117 from the drain bus line 114 as much aspossible so as to make the difference in display characteristics hardlyvisible even when the patterning displacement occurs. However, when theend portions of the pixel electrodes 116, 117 are separated from thedrain bus line 114, regions where the pixel electrodes 116, 117 areformed become narrow and hence, an aperture ratio of the pixel islowered thus giving rise to a drawback that the brightness is lowered.

Further, in laminating the TFT substrate 102 and the counter substrate104 to each other, there may arise a given lamination displacement.Accordingly, it is necessary to make an opening region of a BM 145formed on the counter substrate side narrower than the regions where thepixel electrodes 116, 117 are formed on the TFT substrate 102 side.Accordingly, there arises a drawback that the aperture ratio of thepixels and the brightness are further lowered.

[Patent document 1] Japanese Patent Laid-open Publication H-2 (1990)-12[Patent document 2] U.S. Pat. No. 4,840,460[Patent document 3] Japanese Patent Publication 3076938

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid crystaldisplay device which exhibits high brightness and favorable displayquality.

The above-mentioned object can be achieved by a liquid crystal displaydevice which includes a pair of substrates which are arranged to faceeach other in an opposed manner, vertical-alignment type liquid crystalwhich is sealed between the pair of substrates, a plurality of pixelregions each of which includes a first sub pixel having a first pixelelectrode which is formed on one substrate, and a second sub pixelhaving a second pixel electrode which is formed on one substrate, a slitwhich is formed between the first and the second pixel electrodes, and aprojecting portion or a recessed portion which is formed on an endportion of the first or second pixel electrode on the slit side, whereinthe liquid crystal display device further includes a singular pointcontrol part which controls singular points of the liquid crystal.

According to the present invention, it is possible to provide a liquidcrystal display device which exhibits high brightness and favorabledisplay quality.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a view showing the schematic constitution of a liquid crystaldisplay device according to a first embodiment of the present invention;

FIG. 2 is a view showing the constitution of one pixel of the liquidcrystal display device according to the first embodiment of the presentinvention;

FIG. 3A and FIG. 3B are views showing the constitution of the vicinityof a slit 44 of the liquid crystal display device according to the firstembodiment of the present invention;

FIG. 4A and FIG. 4B are views showing a first modification of a singularpoint control part;

FIG. 5A and FIG. 5B are views showing a second modification of thesingular point control part;

FIG. 6A and FIG. 6B are views showing a third modification of thesingular point control part;

FIG. 7A and FIG. 7B are views showing a fourth modification of thesingular point control part;

FIG. 8A to FIG. 8F are views showing modifications of shapes of aprojecting portion and a recessed portion;

FIG. 9 is a view showing the constitution of one pixel of a liquidcrystal display device according to a second embodiment of the presentinvention;

FIG. 10 is a view showing the constitution of the vicinity of a slit 44of the liquid crystal display device according to the second embodimentof the present invention;

FIG. 11 is a view showing the constitution of the vicinity of the slit44.

FIG. 12 is a view showing a modification of the liquid crystal displaydevice according to the second embodiment of the present invention;

FIG. 13 is a view showing a schematic cross-sectional constitution ofthe conventional liquid crystal display device;

FIG. 14 is a view showing the constitution of one pixel of theconventional liquid crystal display device;

FIG. 15A and FIG. 15B are views for explaining the alignment regulatingstructure;

FIG. 16 is a view for explaining the alignment regulating structure;

FIG. 17 is a view showing the constitution of one pixel of theconventional liquid crystal display device;

FIG. 18 is a cross-sectional view showing the constitution of theconventional liquid crystal display device;

FIG. 19 is a cross-sectional view showing the constitution of theconventional liquid crystal display device;

FIG. 20 is a view schematically showing alignment azimuths of liquidcrystal molecules in respective alignment regions α to δ and an arearatio among the respective alignment regions α to δ in one pixel;

FIG. 21 is a view showing the constitution of one pixel of theconventional liquid crystal display device;

FIG. 22 is a cross-sectional view showing the constitution of theconventional liquid crystal display device;

FIG. 23 is a graph showing the T-V characteristics of a conventional VAmode liquid crystal display device;

FIG. 24A and FIG. 24B are views showing the change of appearance of animage displayed on a display screen;

FIG. 25A to FIG. 25C are views showing gray scale histograms of R, G, Bof a reddish image;

FIG. 26 is a view showing the constitution of one pixel of aconventional MVA method liquid crystal display device using a capacitivecoupling HT method;

FIG. 27 is a view showing the constitution of a pixel electrode in thevicinity of a slit;

FIG. 28 is a view showing a display state of the same region as FIG. 27when a white display is performed by the pixel; and

FIG. 29 is a view schematically showing alignment of liquid crystalmolecules in a region inside a circle P in FIG. 28.

DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

A liquid crystal display device according to a first embodiment of thepresent invention is explained using FIG. 1 to FIG. 8F. As shown in FIG.1, the liquid crystal display device includes a TFT substrate 2 which isprovided with gate bus lines and drain bus lines which are formed in anintersecting manner to each other through an insulation film, and a TFTand a pixel electrode which are formed for every pixel. Further, theliquid crystal display device includes a counter substrate 4 which isarranged to face the TFT substrate 2 in an opposed manner and on whichCFs and a counter electrode are formed, and vertical-alignment-typeliquid crystal which is sealed between both substrates 2, 4 andpossesses negative dielectric anisotropy (not shown in the drawing), forexample. On interfaces of the TFT substrate 2 and the counter substrate4 with the liquid crystal, vertical alignment films (not shown in thedrawing) which align the liquid crystal vertically are formed.

To the TFT substrate 2, a gate bus line drive circuit 80 on which adriver IC for driving a plurality of gate bus lines is mounted and adrain bus line drive circuit 82 on which a driver IC which drives theplurality of drain bus lines is mounted are connected. These drivecircuits 80, 82 are configured to output scanning signals and datasignals to given gate bus lines or given drain bus lines in response togiven signals outputted from a control circuit 84. A polarizer 87 isarranged on a surface opposite to a TFT element forming surface of theTFT substrate 2, while a polarizer 86 which is arranged in a cross-nicolstate with respect to the polarizer 87 is arranged on a surface of thecounter substrate 4 opposite to a surface on which the common electrodeis formed. On surface of the polarizer 87 opposite to the TFT substrate2, a backlight unit 88 is arranged.

FIG. 2 shows the constitution of one pixel of an MVA type liquid crystaldisplay device which uses a capacitive coupling HT method as the liquidcrystal display device according to this embodiment. As shown in FIG. 2,a TFT substrate 2 of the liquid crystal display device includes aplurality of gate bus lines 12 which extend in the lateral direction inFIG. 2 and a plurality of drain bus lines 14 which extend in thevertical direction in FIG. 2 and which are formed in an intersectingmanner through an insulation film (not shown in the drawing). In thevicinity of positions where the gate bus lines 12 and the drain buslines 14 intersect each other, TFTs 20 which are formed for respectivepixels as switching elements are arranged. A gate electrode 23 of theTFT 20 is electrically connected with the gate bus line 12. Anoperational semiconductor layer (not shown in the drawing) is formed onthe gate electrode 23, while a channel protective film 28 is formed onthe operational semiconductor layer. On the channel protective film 28,a rod-like source electrode 22 and a C-shaped drain electrode 21 whichsurrounds the source electrode 22 through a given gap are formed. Thedrain electrode 21 is electrically connected to the drain bus line 14. Aprotective film not shown in the drawing is formed over the wholesubstrate plane in a state that the protective film also covers thesource electrodes 22 and the drain electrodes 21.

Further, a storage capacitor bus line 18 which extends in parallel tothe gate bus line 12 is formed in a state that the storage capacitor busline 18 traverses the pixel region defined by the gate bus lines 12 andthe drain bus lines 14. A storage capacitor electrode 19 is formed onthe storage capacitor bus line 18 through an insulation film for everypixel. The storage capacitor electrode 19 is electrically connected withthe source electrode 22 of the TFT 20 through a control capacitiveelectrode 25. Between the storage capacitor bus line 18 and the storagecapacitor electrode 19, a storage capacitor Cs is formed.

The pixel region includes a sub pixel A and a sub pixel B. The sub pixelA has a trapezoidal shape, for example, and is arranged in a centerportion of the pixel region on a left side. The sub pixel B is arrangedin an upper portion, a lower portion and a right-side end portion of acenter portion in FIG. 2 excluding a region of the sub pixel A out ofthe pixel region. The arrangement of the sub pixels A, B assumes asubstantially line symmetry within one pixel with respect to the storagecapacitor bus line 18. A pixel electrode 16 is formed on the TFTsubstrate 2 in the sub pixel A, while a pixel electrode 17 which isseparated from the pixel electrode 16 is formed on the TFT substrate 2in the sub pixel B. The pixel electrodes 16, 17 are formed of atransparent conductive film, for example, and are formed on the samelayer. The pixel electrode 16 is electrically connected with the storagecapacitor electrode 19 and the source electrode 22 of the TFT 20 via acontact hole 24 formed in a protective film which is formed on thestorage capacitor electrode 19. On the other hand, the pixel electrode17 is held in an electrically floating state. The pixel electrode 17includes a region which faces the control capacitive electrode 25through a protective film in the upper portion of the pixel region inFIG. 2. The pixel electrode 17 is indirectly connected with the sourceelectrode 22 due to a capacitive coupling through a control capacitanceCc of a control capacitance part formed in the region.

The pixel electrodes 16, 17 are separated from each other by slits 44,47, 44 which surround three sides of the trapezoidal pixel electrode 16in an L shape. The slits 44 extend obliquely with respect to an endportion of the pixel region, while the slit 47 extends along aright-side end portion of the pixel region. The slits 44 also functionas the alignment regulating structure which regulates the alignment ofthe liquid crystal. On an end portion of the pixel electrode 17 on theslit 44 side, projecting portions 64 which project in a rectangularshape from the pixel electrode 17 in a substrate plane are formed as asingular point control part which controls the positions of singularpoints in the region above the slit 44. Distal ends of the projectingportions 64 face an end portion of the pixel electrode 16 with a givengap therebetween. The projecting portions 64 are arranged, for example,in the vicinity of the center portion of respective slits 44 in thelongitudinal direction one by one, for example.

The counter substrate 4 which is arranged to face the TFT substrate 2 inan opposed manner with a liquid crystal layer therebetween includes acommon electrode not shown in the drawing which is formed over thesubstantially whole area of the display region. A liquid crystalcapacitance Clc1 is formed between the pixel electrode 16 in the subpixel A and the common electrode which face each other with the liquidcrystal layer therebetween. In the same manner, a liquid crystalcapacitance Clc2 is formed between the pixel electrode 17 in the subpixel B and the common electrode. On the common electrode, a linearprojection 42 which extends in parallel to the slit 44 and obliquelywith respect to the end portion of the pixel region and functions as thealignment regulating structure is formed. The slit 44 and the linearprojection 42 extend in the direction which makes an angle ofapproximately 45° with respect to polarization axes of polarizers 86, 87which are arranged outside in a state that the polarizers 86, 87sandwich the TFT substrate 2 and the counter substrate 4. The linearprojection 42 is formed of a positive resist material such as a novoracresin. The linear projections 42 are arranged in substantially centerportions of the sub pixels A, B respectively so as to uniformly dividethe region which differs in the alignment azimuth of the liquid crystalin the sub pixels A, B. Further, the linear projection 42 is arranged inthe substantially line symmetry in one pixel with respect to the storagecapacitor bus line 18. Due to such a constitution, the liquid crystal inthe sub pixels A and B is substantially uniformly aligned in the fourdirections orthogonal to each other within one pixel. The controlcapacitive electrode 25 which connects the source electrode 22 and thestorage capacitor electrode 19 is arranged on a substrate plane in astate that the control capacitive electrode 25 is overlapped to thelinear projection 42 as viewed vertically. Here, with respect to thepixel electrodes 16, 17, since the defective alignment of the liquidcrystal is liable to easily occur in a region relatively remote from thelinear projection 42 in distance, fine slits 46 which extendsubstantially normal to the direction that the linear projection 42extends are formed in the pixel electrodes 16, 17 in the region. Sincethe liquid crystal is aligned in parallel to the direction that the fineslits 46 extend, the defective alignment of the liquid crystal can besuppressed.

Further, in regions which are arranged in the vicinity of regions wherethe linear projection 42 and the end portions of the pixel electrodes16, 17 intersect and where the extending direction of the linearprojection 42 as viewed normal to the substrate plane and the endportions of the pixel electrodes 16, 17 make an obtuse angle, auxiliaryprojections 43 are formed. The auxiliary projections 43 are formed onthe same layer as the linear projection 42, for example, and extendsubstantially parallel to the drain bus line 14. The auxiliaryprojections 43 are provided for canceling the influence of an electricfield in the vicinity of the end portions of the pixel electrodes 16, 17and are arranged on the end portions of the pixel electrodes 16, 17 inan overlapped manner as viewed normal to the substrate surface. Further,on the counter substrate 4, a BM 45 which shields the image region endportions from light is formed.

Assume that the TFT 20 is turned on so that a voltage is applied to thepixel electrode 16 and a voltage Vpx1 is applied to the liquid crystallayer of the sub pixel A. Here, since the potential is divided inaccordance with the capacitance ratio between the liquid crystalcapacitance Clc2 and the control capacitance Cc, a voltage which isdifferent from a voltage applied to the pixel electrode 16 is applied tothe pixel electrode 17 of the sub pixel B. A voltage Vpx2 which isapplied to the liquid crystal layer of the sub pixel B is expressed asfollows.

Vpx2=(Cc/(Clc2+Cc))×Vpx1

Here, since a relationship 0<(Cc/(Clc2+Cc))<1 is established, thevoltage Vpx2 becomes smaller than the voltage Vpx1 (|Vpx2|<|Vpx1|)except for Vpx1=Vpx2=0. In this manner, in the liquid crystal displaydevice according to this embodiment, it is possible to make the voltageVpx1 applied to the liquid crystal layer in the sub pixel A and thevoltage Vpx2 applied to the liquid crystal layer in the sub pixel Bdifferent from each other in the inside of one pixel. Accordingly, thedistortion of the T-V characteristics can be dispersed in one pixel andhence, a phenomenon that the color of the image as viewed from theoblique direction becomes whitish can be suppressed thus realizing theacquisition of the liquid crystal display device of a wide viewing anglewhich can improve the viewing angle characteristics.

Further, in this embodiment, in the vicinity of an end portion of thepixel electrode 16 which faces the drain bus line 14 (a left-side endportion in FIG. 2), a light shielding plate 54 which extends along theend portion is formed. The light shielding plate 54 has a function ofshielding the vicinity of the end portion from the light. Further, thelight shielding plate 54 is formed on the same layer as the storagecapacitor bus line 18 and is electrically connected with the storagecapacitor bus line 18. For example, the light shielding plate 54 isbranched from the storage capacitor bus line 18. Accordingly, the lightshielding plate 54 is held at the same potential (common potential) asthe storage capacitor bus line 18 and the common electrode and hence, avoltage is not applied to the liquid crystal layer in the vicinity ofthe region where the light shielding plate 54 is formed whereby theoccurrence of leaking of light or the like can be suppressed in thenormally black-mode liquid crystal display device.

Since the light shielding plate 54 is formed on the TFT substrate 2side, it is unnecessary to take the lamination displacement intoconsideration. Accordingly, it is possible to arrange the lightshielding plate 54 outside the BM 45 as viewed normal to the substrateplane and, at the same time, in the region where the light shieldingplate 54 is formed, it is possible to arrange the end portion of theBM45 outside by an amount of width d1. As viewed normal to the substrateplane, a distance between the end portion of the BM45 in the regionwhere the light shielding plate 54 is formed and the drain bus line 14is set narrower than a distance between the end portion of the BM45 inother region and the drain bus line 14.

Further, the light shielding plate 54 and the pixel electrode 16 arearranged in an overlapped manner. Further, with the provision of thelight shielding plate 54, the influence of an electric capacitance whichis generated between the drain bus line 14 and the pixel electrode 16can be suppressed and hence, even when the pixel electrode 16 isarranged close to the drain bus line 14, a defective display attributedto crosstalk is hardly generated. On the other hand, when the pixelelectrode 17 which is connected to the source electrode 22 due tocapacitive coupling and the light shielding plate 54 are arranged to beoverlapped to each other, a new electric capacitance is generatedbetween the pixel electrode 17 and the light shielding plate 54 andhence, the light shielding plate 54 is not formed in the vicinity of theend portion of the pixel electrode 17 which faces the drain bus line 14in an opposed manner. As a result of these arrangement andconsideration, a distance between the end portion of the pixel electrode16 which faces the drain bus line 14 in an opposed manner and the drainbus line 14 is set narrower than a distance between the end portion ofthe pixel electrode 17 which faces the drain bus line 14 in an opposedmanner and the drain bus line 14 by an amount of a width d2. In thismanner, according to this embodiment, with the provision of the lightshielding plate 54, it is possible to enhance an aperture ratio of thepixel and hence, it is possible to acquire the liquid crystal displaydevice having the high brightness.

Next, the alignment of the liquid crystal in the region above the slit44 of the liquid crystal display device according to this embodiment isexplained. FIG. 3A shows the constitution in the vicinity of the slit 44of the pixel (in FIG. 3A, two projecting portions 64 are formed.). FIG.3B shows a display state of the same region as FIG. 3A when the pixel isallowed to perform a white display. As shown in FIG. 3A and FIG. 3B, inthe vicinity of the region where the projecting portion 64 whichprojects from the pixel electrode 17 as a singular point control part isformed, liquid crystal molecules 8 on the pixel electrodes 16, 17 aretilted in the direction toward the outside from the slit 44, while theliquid crystal molecules 8 on the slit 44 are tilted in the directiontoward the projecting portion 64. Accordingly, in the regions where theprojecting portion 64 is formed, singular points 62 b (s=−1) are firmlyformed respectively. Positions of the singular points 62 b are neitherchanged even along with the different voltage applying histories normoved along with the lapse of time. Between two singular points 62 b, asingular point 62 a (s=+1) is formed. Although a position of thesingular point 62 a may be changed along with the different voltageapplying histories, for example, since a range within which the positionis changed is limited to a span between two projecting portions 64,there exists no possibility that the display quality is largelydegraded. The neighboring singular points 62 b, 62 b, are connected bytwo dark lines which respectively extend along the slit-44-side endportions of the pixel electrodes 16, 17.

FIG. 4A shows a first modification of the singular point control parts.FIG. 4B shows a display state of the same region as FIG. 4A when thepixel is allowed to perform a white display. As shown in FIG. 4A andFIG. 4B, the singular point control parts of the modification includeprojecting portions 65 formed on a slit-44-side end portion of the pixelelectrode 16 of the sub pixel A. Also in this embodiment, singularpoints 62 b are formed in regions where the projecting portions 65 arefirmly formed, and a singular point 62 a is formed between the singularpoints 62 b.

FIG. 5A shows a second modification of the singular point control parts.FIG. 5B shows a display state of the same region as FIG. 5A when thepixel is allowed to perform a white display. As shown in FIG. 5A andFIG. 5B, the singular point control parts of the modification includeprojecting portions 64 formed on a slit-44-side end portion of the pixelelectrode 17 and projecting portions 65 formed on a slit-44-side endportion of the pixel electrode 16. The projecting portions 64 and theprojecting portions 65 are arranged such that respective distal endportions thereof face each other in an opposed manner with a given gaptherebetween. Also in this modification, singular points 62 b are firmlyformed in regions where the projecting portions 64, 65 are formed, and asingular point 62 a is formed between the singular points 62 b.

FIG. 6A shows a third modification of the singular point control part.FIG. 6B shows a display state of the same region as FIG. 6A when thepixel is allowed to perform a white display. As shown in FIG. 6A andFIG. 6B, the singular point control part of this modification includesrecessed portions 66 which are notched in a rectangular shape in aslit-44-side end portion of the pixel electrode 17 in a substrate plane,and recessed portions 67 which are notched in the same manner in aslit-44-side end portion of the pixel electrode 16 in a substrate plane.The recessed portions 66, 67 are arranged at positions where therecessed portions 66, 67 face each other in an opposed manner. In thismodification, in the vicinity of regions where the recessed portions 66,67 are formed, liquid crystal molecules 8 on the pixel electrodes 16, 17are tilted in the direction toward the outside from the slit 44, whilethe liquid crystal molecules 8 on the slit 44 are tilted in thedirection parallel to the extending direction of the slit 44 as well asin the direction toward the outside from the recessed portions 66, 67.Accordingly, in the regions where the recessed portions 66, 67 areformed, singular points 62 a (s=+1) are firmly formed. Positions of thesingular points 62 a are neither changed even along with the differencevoltage applying histories nor moved along with the lapse of time.Between two singular points 62 a, a singular point 62 b (s=−1) isformed. Although a position of the singular point 62 b may be changedalong with the different voltage applying histories, for example, sincea range within which the position is changed is limited to a spanbetween two singular points 62 a, there exists no possibility that thedisplay quality is largely degraded.

FIG. 7A shows a fourth modification of the singular point control parts.FIG. 7B shows a display state of the same region as FIG. 7A when thepixel is allowed to perform a white display. As shown in FIG. 7A andFIG. 7B, the singular point control parts of the modification includeprojecting portions 64 formed on a slit-44-side end portion of the pixelelectrode 17 and recessed portions 67 formed on a slit-44-side endportion of the pixel electrode 16. The projecting portions 64 and therecessed portions 67 are arranged such that respective distal endportions thereof face each other in an opposed manner. In thismodification, in the vicinity of regions where the projecting portions64 and the recessed portions are formed, liquid crystal molecules 8 onthe pixel electrodes 16, 17 are tilted in the direction toward theoutside from the slit 44, while the liquid crystal molecules 8 on theslit 44 are tilted in the direction toward the outside from theprojecting portions 64. Accordingly, in the regions where the projectingportions 64 and the recessed portions 67 are formed, the singular points62 b are firmly formed. Between two singular points 62 b, a singularpoint 62 a is formed.

To compare the constitutions shown in FIG. 3A to FIG. 7B, theconstitution which forms the projecting portions 64 on the pixelelectrode 17 of the sub pixel B as shown in FIG. 3A and FIG. 3B isrelatively excellent in view of the stability of the singular points andthe high optical transmissivity at the time of applying a voltage. Thatis, when the voltage applied to the liquid crystal layer differs forevery sub pixel, it is desirable that the projecting portions are formedon the pixel electrode of the sub pixel where a magnitude of a voltageapplied to the liquid crystal layer is small.

By forming the singular point control parts as shown in FIG. 3A to FIG.7B, the singular points 62 b (or 62 a) are firmly formed, and thesingular point 62 a (or 62 b) is formed between singular points 62 b (or62 a). Accordingly, the positions where the singular points 62 a, 62 bare formed can be substantially fixed spatially and for a long periodand hence, even after passing the different voltage applying histories,there is no possibility that the positions of the singular points 62 a,62 b are changed whereby a phenomenon that a display differs dependingon the screen viewing direction can be obviated. Further, since thesingular points 62 b (or 62 a) are firmly formed, even when thealignment of the liquid crystal is disturbed due to the localapplication of pressure to a display screen by finger pushing or thelike and the alignment of the liquid crystal is disturbed, it ispossible to easily restore the original alignment state. In this manner,according to the above-mentioned embodiments, it is possible to obtainthe liquid crystal display device which exhibits the favorable displaycharacteristics.

Here, shapes of the projecting portions 64, 65 and the recessed portions66, 67 are not limited to the rectangular shape shown in FIG. 3A to FIG.7B. FIG. 8A to FIG. 8F show modification of the shapes of the projectingportions 64, 65 and the recessed portions 66, 67. In an example shown inFIG. 8A, the projecting portion 64 and/or 65 has a triangular shape. Inan example shown in FIG. 8B, the recessed portion 66 and/or 67 has atriangular shape. In an example shown in FIG. 8C, the projecting portion64 and/or 65 has a step-like shape. In an example shown in FIG. 8D, therecessed portion 66 and/or 67 has a step-like shape. In an example shownin FIG. 8E, the projecting portion 64 and/or 65 has a semicircularshape. In an example shown in FIG. 8F, the recessed portion 66 and/or 67has a semicircular shape. The projecting portions 64, and the recessedportions 66, 67 may be formed in various shapes besides theabove-mentioned shapes.

Further, in the modifications shown in FIG. 5A to FIG. 78, theprojecting portions 64 or the recessed portions 66 which are formed onor in the pixel electrode 17 and the projecting portions 65 or therecessed portions 67 which are formed on or in the pixel electrode 16are arranged at positions where these portions face each other in anopposed manner. However, in this embodiment, it is possible to modifysuch arrangements and adopt arrangements in which the positions of theprojecting portions 64 or the recessed portions 66 and the positions ofthe projecting portions 65 or the recessed portions 67 are displacedfrom each other. It is needless to say that the positions and thecombinations of the projecting portions 64 or the recessed portions 66and the projecting portions 65 or the recessed portions 67 are notlimited to the examples shown in FIG. 3A to FIG. 7B and variousmodifications can be made. For example, by alternatively arranging theprojecting portions 64, 65 shown in FIG. 5A and FIG. 5B with therecessed portions 66, 67 shown in FIG. 6A and FIG. 6B, both positionswhere the singular points 62 a (s=+1), 62 b (s=−1) are formed are fixed.

Second Embodiment

Next, a liquid crystal display device according to the second embodimentof the present invention is explained in conjunction with FIG. 9 to FIG.12. FIG. 9 shows the constitution of one pixel of the liquid crystaldisplay device according to this embodiment, and FIG. 10 shows theconstitution of the vicinity of a slit 44 of the liquid crystal displaydevice according to this embodiment. As shown in FIG. 9 and FIG. 10, incomparison with the first embodiment, this embodiment is characterizedin that an auxiliary electrode 68 extends in the substantially samedirection as the extending direction of the slits 44, 47 is formed onthe slits 44, 47 in an overlapped manner. The auxiliary electrode 68 isformed on the same layer as the storage capacitor bus line 18 and iselectrically connected with the storage capacitor bus line 18 and isbranched from the storage capacitor bus line 18, for example. Further,the auxiliary electrode 68 is also connected with a light shieldingplate 54 which is formed on an end portion which faces a drain bus line14 of a pixel electrode 16 in an opposed manner. When a pixel electrode17 which is connected with the source electrode 22 due to capacitivecoupling and the auxiliary electrode 68 are arranged in an overlappedmanner, a new electric capacitance is generated between the pixelelectrode 17 and the auxiliary electrode 68 and hence, the auxiliaryelectrode 68 is formed in a state that the auxiliary electrode 68 is notoverlapped to the pixel electrode 17.

The auxiliary electrode 68 is held at the same potential (commonpotential) as the storage capacitor bus line 18 and the commonelectrode. Accordingly, even when a given voltage is applied to theliquid crystal layers of the sub pixels A, B respectively, the voltageis not applied to the liquid crystal layer in the vicinity of the regionin which the auxiliary electrode 68 is formed and hence, the liquidcrystal molecules 8 in the region hold the alignment substantiallynormal to the substrate plane. By forming the auxiliary electrode 68 onthe slits 44, 47 in an overlapped manner, the liquid crystal molecules 8on the slits 44, 47 are not tilted and hence, there is no possibilitythat singular points are formed. Accordingly, degradation of the displayquality attributed to the fact that the positions of the singular pointsare not fixed is not generated basically and hence, it is possible toobtain a liquid crystal display device having favorable display quality.

The slit 44 arranged between the pixel electrodes 16, and the auxiliaryelectrode 68 is formed using a photolithography method. When a relativepositional displacement takes place between the slit 44 and theauxiliary electrode 68 due to the patterning displacement or the like,there may be a case that the auxiliary electrode 68 is displaced fromthe center portion of the slit 44. In such a case, when the voltage isapplied to the liquid crystal layer in the sub pixels A and B, theliquid crystal molecules 8 on the slits 44, 47 are tilted and hence, thesingular points are formed. Accordingly, in this embodiment, to fix thesingular point even when the singular points are formed, a projectingportion 64 is mounted on an slit-44-side end portion of the pixelelectrode 17 of the sub pixel B. Accordingly, even when a relativepositional displacement is generated between the slit 44 and theauxiliary electrode 68, it is possible to obtain a liquid crystaldisplay device having favorable display quality and hence, a yield ratein manufacturing the liquid crystal display device is enhanced.

However, in the constitution provided with the projecting portion 64,when the positional displacement shown in FIG. 11 is generated betweenthe slit 44 and the auxiliary electrode 68, for example, a region Cwhere the auxiliary electrode 68 does not exist is formed between thedistal end portion of the projecting portion 64 and the pixel electrode16. Since the auxiliary electrode 68 does not exist in the region C anda distance between the pixel electrodes 16, 17 is relatively small, whena display screen is locally pressed by pushing using a finger or thelike, there arises a drawback that the alignments of the liquid crystalin the sub pixels A, B are connected thus giving rise to a drawback thatthe defective alignment occurs.

FIG. 12 shows a modification of the auxiliary electrode 68 which cansolve the above-mentioned drawback. As shown in FIG. 12, the auxiliaryelectrode 68 has a protruding portion 69 which projects in the samedirection as the projection direction of the projecting portion 64 inthe region corresponding to the projecting portion 64 of the pixelelectrode 17. The protruding portion 69 is formed to have a width largerthan a width of the projecting portion 64. With the provision of theprotruding portion 69, even when the positional displacement shown inFIG. 11 is generated between the slit 44 and the auxiliary electrode 68,a region where the auxiliary electrodes 68 does not exist is not formedbetween the distal end portion of the projecting portion 64 and thepixel electrode 16. Accordingly, the defective alignment of the liquiddisplay hardly occurs and hence, it is possible to obtain the liquidcrystal display device having a favorable display quality. Here, whenthe projecting portions 64, 65 which face each other are formed as shownin FIG. 5A and FIG. 5B, the protruding portion 69 is formed on bothsides of the auxiliary electrode 68.

The present invention is not limited to the above-mentioned embodimentand various modifications can be made.

For example, although a transmissive liquid crystal display device hasbeen explained as an example in the above-mentioned embodiments, thepresent invention is not limited to such a display device and isapplicable to other liquid crystal display device such as a reflectiveliquid crystal display device or a transflective liquid crystal displaydevice.

Further, in the above-mentioned embodiment, a liquid crystal displaydevice in which a pixel region includes two sub pixels has beenexplained as an example, the present invention is not limited to such adisplay device. That is, the present invention is applicable to a liquidcrystal display device in which a pixel region includes three or moresub pixels.

Further, although a liquid crystal display device which adopts acapacitance coupling HT method in which the voltage applied to theliquid crystal layer differs for every each sub pixel has been explainedin the above-mentioned embodiments, the present invention is not limitedto such a display device. That is, the present invention is applicableto a general MVA type liquid crystal display device in which voltageswhich are applied to the liquid crystal layers in a plurality of subpixels within one pixel which is divided using the slit aresubstantially set equal with each other.

1. A liquid crystal display device comprising: a pair of substrateswhich are arranged to face each other in an opposed manner;vertical-alignment type liquid crystal which is sealed between the pairof substrates; a plurality of pixel regions, each pixel region includinga first sub pixel having a first pixel electrode on one substrate and asecond sub pixel having a second pixel electrode on one substrate, aslit formed between the first and second pixel electrodes; and asingular point control part which includes a projecting portion and/or arecessed portion which is/are formed on an end portion of the firstand/or second pixel electrode on the slit-side and controls singularpoints of the liquid crystal. 2-16. (canceled)